Two huge hedge funds run by Paul Tudor Jones's Tudor Investment Corp., which manages more than $20 billion, suffered sizable losses in July. The Raptor Fund, a $9 billion hedge fund run by James Pallotta in Boston, dropped 9% in the month, and is down almost 3% so far in 2007, according to investors. The fund that Mr. Jones runs in Greenwich, Conn., the $10.3 billion Tudor BVI Fund, lost just over 3% in July, though it is up 4.6% for the year.

The losses are surprising because both managers have among the best track records in the hedge-fund world. Some investors said the results were disappointing, but noted that Mr. Jones has scored an average annual return of over 24% since launching his fund in 1986, while Mr. Pallotta has generated gains of over 19% since 1993.

Investors have been waiting to see how hedge funds fared in July, a difficult month in various markets that saw $3 billion hedge fund Sowood Capital collapse after losing more than 50% of their assets.